1. Field of the Invention
The present invention relates to a silicon oxide film, and particularly to a silicon oxide film having superior electric characteristics as a gate insulation film and a production method therefor. The present invention also relates to a semiconductor device, an active-matrix substrate and an electronic device, which are provided with the silicon oxide film as the gate insulation film.
2. Description of the Related Art
It is well-known to use a thin film transistor (TFT) formed on an insulative substrate such as a glass substrate as a driving device of an active-matrix type of a liquid-crystal display panel. In recent years, the TFT having high durability and high reliability is needed due to the tendency of imparting many functions to and microfabricating a semiconductor device containing the TFT. It is particularly important to suppress the variation of a threshold value (Vth) of the TFT, which occurs when voltage has been applied to a gate electrode for many hours. The variation of electric characteristics caused by an electric stress due to the voltage application on the TFT for many hours, that is to say, the reliability of the TFT is known to have a relationship with characteristics of the gate insulation film. In order to improve the reliability of the gate insulation film, for instance, there is such a technique as is described in Patent Document 1, which suppresses the variation of the Vth of the TFT by inhibiting the gate insulation film from trapping an electric charge which has been injected into the gate insulation film when the voltage has been applied to a gate electrode, by blending carbon in the gate insulation film which is mainly formed of a silicon oxide film and reducing a charge trapping level.
There is water (H2O) as another impurity which exerts an effect on electric characteristics of the gate insulation film. It is well known as is described in Patent Document 2 that when a large amount of H2O exists in the gate insulation film, for instance, the electric characteristics of the gate insulation film are deteriorated and the variation of the electric characteristics of the TFT with the use of such a gate insulation film increases due to the voltage application.    [Patent Document 1] Japanese Patent Laid-Open No. 2001-135822 (23rd lines in right column on page 2)    [Patent Document 2] Japanese Patent Laid-Open No. 10-321619 (35th lines in right column on page 2)
However, the TFT disclosed in Patent Document 1 has such problems as will be described below. The problem is that when the carbon in the gate insulation film exists in such a state of having high electroconductivity as that of graphite, an electric current may flow through the gate insulation film when the voltage is applied to the gate electrode, and rather deteriorate the gate isolation voltage. It is also known from an experiment by the present inventors that when an organosilane is used for forming the gate insulation film and many intermediate products containing carbon which has been produced due to an insufficient decomposition of the organosilane exist, the phenomenon becomes remarkable. For this reason, the method of simply making carbon exist in the gate insulation film did not show a sufficient effect of reducing the variation of electric characteristics of the TFT, which occurs when voltage is applied to the gate electrode of the TFT for many hours.
On the other hand, when the TFT is formed on a glass substrate, a high-temperature process (for instance, 1,000° C. or higher) cannot be applied, so that H2O which has been produced or has been taken from outside while the TFT is formed is not completely eliminated and remains in the TFT to some extent. For this reason, it has been difficult to reduce the variation of the electric characteristics of the TFT.
An object of the present invention is to provide a silicon oxide film which can be a high-performance gate insulation film, by solving the above described problems.